Index: tests/Zend/JsonTest.php
===================================================================
--- tests/Zend/JsonTest.php	(revision 14252)
+++ tests/Zend/JsonTest.php	(working copy)
@@ -443,6 +443,18 @@
 
     	$this->assertEquals('{"firstName":"John","lastName":"Doe","email":"john@doe.com"}', $result);
     }
+
+    public function testToJsonEmbededObjectSerialization()
+    {
+        $contacts = array(
+            new ToJsonClass()
+        );
+
+        Zend_Json::$useBuiltinEncoderDecoder = true;
+        $result = Zend_Json::encode($contacts);
+
+        $this->assertEquals('[{"firstName":"John","lastName":"Doe","email":"john@doe.com"}]', $result);
+    }
     
     public function testIteratorToJson()
     {
Index: library/Zend/Json/Encoder.php
===================================================================
--- library/Zend/Json/Encoder.php	(revision 14252)
+++ library/Zend/Json/Encoder.php	(working copy)
@@ -133,6 +133,11 @@
             $this->_visited[] = $value;
         }
 
+        if (method_exists($value, 'toJson'))
+        {
+            return $value->toJson();
+        }
+
         $props = '';
 
         if ($value instanceof Iterator) {